1. Field of the Invention
This invention relates to persistent data and more particularly relates to maintaining dynamic persistent data.
2. Description of the Related Art
Mission critical data processing devices such as high-availability hard disk drive arrays often employ one or more redundant elements to eliminate single points of failure. For example, a high-availability hard disk drive array may include two controller cards. Each controller card may be configured to access all of the hard disk drives in the array. Thus if a first controller card failed, a second controller card could continue to provide access to the hard disk drive array.
Some data processing device elements may not have redundant counterparts. For example, a backplane may be considered passive and so not require a redundant counterpart.
Data such as configuration data may be stored in a plurality of service controller card non-volatile storage devices (NSD). If the data in a first service controller card NSD may become corrupted, the data may be retrieved from a second service controller card NSD.
Unfortunately, it may be difficult to determine whether the first service controller card NSD data or the second service controller card NSD data is corrupted. As a result, three or more copies of the data may be stored. For example, in addition to the service controller card NSD, one or more backplane NSD may store the data. The backplane NSD data may be compared with the data from the first and second service controller card NSD data. The data instance stored in a quorum of devices such as three devices may be considered valid data.
One or more backplane NSD may be embodied in a backplane. Periodically, the data stored in the backplane NSD and service controller card NSD may need to be updated. Unfortunately, updating the data may temporarily make it impossible to determine which instance of data is valid from a quorum of the service controller card NSD and backplane NSD.